Avalanche Forecast

Issued: Feb 8th, 2018 5:18PM

The alpine rating is high, the treeline rating is high, and the below treeline rating is considerable. Known problems include Storm Slabs and Persistent Slabs.

Avalanche Canada cgarritty, Avalanche Canada

Reactive new storm slabs have formed over a snowpack that is capable of producing very large avalanches. A Special Avalanche Warning is in effect in this region. Copy this address to view details: http://bit.ly/2nSOUyX

Summary

Confidence

High -

Weather Forecast

Friday: A mix of sun and cloud. Light north winds. Freezing level returning to valley bottom with alpine high temperatures to around -12.Saturday: Mainly sunny with lingering valley cloud due to an alpine temperature inversion. Light northwest winds. Alpine high temperatures to around -9. Cooler at lower elevations.Sunday: Mainly sunny with some valley cloud due to a lingering alpine temperature inversion. Light southwest winds. Alpine high temperatures around -8. Temperature inversion breaking down overnight.

Avalanche Summary

Wednesday's reports included observations of storm slabs releasing naturally as well as with ski cutting and explosives generally from size 1-2, with a couple of outliers at sizes 2.5 and 3. No new persistent slab releases were reported in the South Columbias.Many avalanches were reported in the region on Tuesday. Storm and wind slabs were 20 to 50 cm deep, but as deep as 100 cm in wind-loaded features, on all aspects, at all elevations, and triggered naturally, by explosives, and skiers. Persistent slab avalanches often released on the mid-December layer, between 100 and 250 cm deep.Monday's reports showed widespread avalanche activity involving storm, wind, and persistent slabs. The persistent slabs released on all of the weak layers described below, between 100 and 400 cm deep, and on all aspects.Expect dangerous snowpack conditions to persist on Friday as our snowpack adjusts to the new load. A stable weather pattern in the forecast suggests we may see a decrease in natural avalanches, but human triggering remains a big concern. Storm and wind slabs also have the potential to step down to deeper weak layers, which could produce very large avalanches with high consequences.

Snowpack Summary

Around 30-40 cm of snow fell during Wednesday's storm. 130-240 cm storm snow totals from the past two weeks have now consolidated into a deep slab over four active weak layers:1) 130 to 240 cm of storm snow sits on the crust and/or surface hoar layer from mid-January. The crust is widespread, with the exception of high elevation north aspects. The surface hoar was reported up to tree line and possibly higher. This layer is our primary weak layer of concern, partially for remaining nearest to the depth range of human triggering.2) The early-January persistent weak layer is 160 to 260 cm deep. It is composed of surface hoar on sheltered slopes as well as sun crust on steep solar aspects and is found at all elevation bands.3) Another weak layer buried mid-December consists of a facet/surface hoar/crust combination, which is buried 170 to 280 cm deep. It is most problematic at and below tree line.4) A crust/facet layer from late November is yet another failure plane responsible for recent very large avalanches.The wide distribution and ongoing reactivity of these layers suggests that choosing simple terrain free of overhead hazard is the best avoidance strategy.

Problems

Storm Slabs

An icon showing Storm Slabs
Heavy snowfall and steady winds have formed thick new storm slabs on the surface. As the new snow consolidates, potential for human triggering storm slabs will increase. Strong solar effect may act as a trigger for natural avalanches on Friday.
If triggered, storm slabs may step down to deeper layers and result in large avalanches.Choose low-angled, sheltered terrain where new snow hasn't been wind-affected.Avoid exposure to sun-exposed slopes.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

Persistent Slabs

An icon showing Persistent Slabs
Several unstable weak layers are lurking deep in our snowpack. These layers have the potential to be triggered both naturally and with skier or rider traffic. When triggered, these layers have been producing very large avalanches that can run far.
Avoid the runout zones of avalanche paths. Avalanches could run full path.Use conservative route selection. Choose low-angle, supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 4

Valid until: Feb 9th, 2018 2:00PM